Re: [PATCH v7 5/5] loop: Add support for provision requests

Darrick J. Wong
2023-05-23T01:23:01Z

On Mon, May 22, 2023 at 03:09:55PM -0700, Sarthak Kukreti wrote:
> On Mon, May 22, 2023 at 9:37 AM Darrick J. Wong <djwong@kernel.org> wrote:
> >
> > If someone calls fallocate(UNSHARE_RANGE) on a loop bdev, shouldn't
> > there be a way to pass that through to the fallocate call to the backing
> > file?
> >
> > --D
> >
>
> Yeah, I think we could add a REQ_UNSHARE bit (similar to REQ_NOUNMAP) to pass down the intent to the backing file (and possibly beyond...).
>
> I took a stab at implementing it as a follow up patch so that there's
> less review churn on the current series. If it looks good, I can add
> it to the end of the series (or incorporate this into the existing
> block and loop patches):

It looks like a reasonable addition to the end of the series, assuming
that filling holes in thinp devices is cheap but unsharing snapshot
blocks is not.

> From: Sarthak Kukreti <sarthakkukreti@chromium.org>
> Date: Mon, 22 May 2023 14:18:15 -0700
> Subject: [PATCH] block: Pass unshare intent via REQ_OP_PROVISION
>
> Allow REQ_OP_PROVISION to pass in an extra REQ_UNSHARE bit to
> annotate unshare requests to underlying layers. Layers that support
> FALLOC_FL_UNSHARE will be able to use this as an indicator of which
> fallocate() mode to use.

> Signed-off-by: Sarthak Kukreti <sarthakkukreti@chromium.org>
> ---
> block/blk-lib.c | 6 +++++-
> block/fops.c | 6 +++++-
> drivers/block/loop.c | 35 +++++++++++++++++++++++++++++------
> include/linux/blk_types.h | 3 +++
> include/linux/blkdev.h | 3 ++-
> 5 files changed, 44 insertions(+), 9 deletions(-)
>
> diff --git a/block/blk-lib.c b/block/blk-lib.c
> index 3cff5fb654f5..bea6f5a700b3 100644
> --- a/block/blk-lib.c
> +++ b/block/blk-lib.c
> @@ -350,6 +350,7 @@ EXPORT_SYMBOL(blkdev_issue_secure_erase);
> * @sector: start sector
> * @nr_sects: number of sectors to provision
> * @gfp_mask: memory allocation flags (for bio_alloc)
> + * @flags: controls detailed behavior
> *
> * Description:
> * Issues a provision request to the block device for the range of sectors.
> @@ -357,7 +358,7 @@ EXPORT_SYMBOL(blkdev_issue_secure_erase);
> * underlying storage pool to allocate space for this block range.
> */
> int blkdev_issue_provision(struct block_device *bdev, sector_t sector,
> - sector_t nr_sects, gfp_t gfp)
> + sector_t nr_sects, gfp_t gfp, unsigned flags)
> {
> sector_t bs_mask = (bdev_logical_block_size(bdev) >> 9) - 1;
> unsigned int max_sectors = bdev_max_provision_sectors(bdev);
> @@ -380,6 +381,9 @@ int blkdev_issue_provision(struct block_device *bdev, sector_t sector,
> bio->bi_iter.bi_sector = sector;
> bio->bi_iter.bi_size = req_sects << SECTOR_SHIFT;
>
> + if (flags & BLKDEV_UNSHARE_RANGE)

This is a provisioning flag, shouldn't this be ...
BLKDEV_PROVISION_UNSHARE or something?

> + bio->bi_opf |= REQ_UNSHARE;
> +
> sector += req_sects;
> nr_sects -= req_sects;
> if (!nr_sects) {
> diff --git a/block/fops.c b/block/fops.c
> index be2e41f160bf..6848756f0557 100644
> --- a/block/fops.c
> +++ b/block/fops.c
> @@ -659,7 +659,11 @@ static long blkdev_fallocate(struct file *file, int mode, loff_t start,
> case FALLOC_FL_KEEP_SIZE:
> case FALLOC_FL_UNSHARE_RANGE | FALLOC_FL_KEEP_SIZE:
> error = blkdev_issue_provision(bdev, start >> SECTOR_SHIFT,
> - len >> SECTOR_SHIFT, GFP_KERNEL);
> + len >> SECTOR_SHIFT, GFP_KERNEL,
> + (mode &
> + FALLOC_FL_UNSHARE_RANGE) ?
> + BLKDEV_UNSHARE_RANGE :
> + 0);

You might want to do something about the six level indent here;
Linus hates that.

--D

> break;
> case FALLOC_FL_ZERO_RANGE:
> case FALLOC_FL_ZERO_RANGE | FALLOC_FL_KEEP_SIZE:
> diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> index 7fe1a6629754..c844b145d666 100644
> --- a/drivers/block/loop.c
> +++ b/drivers/block/loop.c
> @@ -306,6 +306,30 @@ static int lo_read_simple(struct loop_device *lo, struct request *rq,
> return 0;
> }
>
> +static bool validate_fallocate_mode(struct loop_device *lo, int mode)
> +{
> + bool ret = true;
> +
> + switch (mode) {
> + case FALLOC_FL_PUNCH_HOLE:
> + case FALLOC_FL_ZERO_RANGE:
> + if (!bdev_max_discard_sectors(lo->lo_device))
> + ret = false;
> + break;
> + case 0:
> + case FALLOC_FL_UNSHARE_RANGE:
> + if (!bdev_max_provision_sectors(lo->lo_device))
> + ret = false;
> + break;
> +
> + default:
> + ret = false;
> + }
> +
> + return ret;
> +}
> +
> +
> static int lo_fallocate(struct loop_device *lo, struct request *rq, loff_t pos,
> int mode)
> {
> @@ -316,11 +340,7 @@ static int lo_fallocate(struct loop_device *lo, struct request *rq, loff_t pos,
> struct file *file = lo->lo_backing_file;
> int ret;
>
> - if (mode & (FALLOC_FL_PUNCH_HOLE | FALLOC_FL_ZERO_RANGE) &&
> - !bdev_max_discard_sectors(lo->lo_device))
> - return -EOPNOTSUPP;
> -
> - if (mode == 0 && !bdev_max_provision_sectors(lo->lo_device))
> + if (!validate_fallocate_mode(lo, mode))
> return -EOPNOTSUPP;
>
> mode |= FALLOC_FL_KEEP_SIZE;
> @@ -493,7 +513,10 @@ static int do_req_filebacked(struct loop_device *lo, struct request *rq)
> case REQ_OP_DISCARD:
> return lo_fallocate(lo, rq, pos, FALLOC_FL_PUNCH_HOLE);
> case REQ_OP_PROVISION:
> - return lo_fallocate(lo, rq, pos, 0);
> + return lo_fallocate(lo, rq, pos,
> + (rq->cmd_flags & REQ_UNSHARE) ?
> + FALLOC_FL_UNSHARE_RANGE :
> + 0);
> case REQ_OP_WRITE:
> if (cmd->use_aio)
> return lo_rw_aio(lo, cmd, pos, ITER_SOURCE);
> diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
> index b7bb0226fdee..1a536fd897cb 100644
> --- a/include/linux/blk_types.h
> +++ b/include/linux/blk_types.h
> @@ -423,6 +423,8 @@ enum req_flag_bits {
> */
> /* for REQ_OP_WRITE_ZEROES: */
> __REQ_NOUNMAP, /* do not free blocks when zeroing */
> + /* for REQ_OP_PROVISION: */
> + __REQ_UNSHARE, /* unshare blocks */
>
> __REQ_NR_BITS, /* stops here */
> };
> @@ -451,6 +453,7 @@ enum req_flag_bits {
> #define REQ_FS_PRIVATE (__force blk_opf_t)(1ULL << __REQ_FS_PRIVATE)
>
> #define REQ_NOUNMAP (__force blk_opf_t)(1ULL << __REQ_NOUNMAP)
> +#define REQ_UNSHARE (__force blk_opf_t)(1ULL << __REQ_UNSHARE)
>
> #define REQ_FAILFAST_MASK \
> (REQ_FAILFAST_DEV | REQ_FAILFAST_TRANSPORT | REQ_FAILFAST_DRIVER)
> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> index 462ce586d46f..60c09b0d3fc9 100644
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -1049,10 +1049,11 @@ int blkdev_issue_secure_erase(struct block_device *bdev, sector_t sector,
> sector_t nr_sects, gfp_t gfp);
>
> extern int blkdev_issue_provision(struct block_device *bdev, sector_t sector,
> - sector_t nr_sects, gfp_t gfp_mask);
> + sector_t nr_sects, gfp_t gfp_mask, unsigned int flags);
>
> #define BLKDEV_ZERO_NOUNMAP (1 << 0) /* do not free blocks */
> #define BLKDEV_ZERO_NOFALLBACK (1 << 1) /* don't write explicit zeroes */
> +#define BLKDEV_UNSHARE_RANGE (1 << 2) /* unshare range on provision */
>
> extern int __blkdev_issue_zeroout(struct block_device *bdev, sector_t sector,
> sector_t nr_sects, gfp_t gfp_mask, struct bio **biop,
> --
> 2.39.2
>